Touch screens can be classified into four types of touch screen, such as a resistive film type (pressure sensitive type) touch screen, a capacitive type touch screen, a surface acoustic wave (SAW) type touch screen, and an infrared ray (IR) type touch screen.
The pressure sensitive type (resistive film type) touch screen among them means literally a touch screen that operates by recognizing pressure. The operating principle of the pressure sensitive type touch screen is implemented by applying a material having a resistive component onto glass or a transparent plastic plate, covering the material with a polyethylene (PE) film and installing insulation rods at regular intervals so that two surfaces of the glass or transparent plastic plate are not in contact with each other. In an operating state, if a predetermined current flows through both ends of a resistive film, the resistive film serves as a resistor having a resistive component and thus, a voltages is applied between both ends of the resistive film. If the resistive film is touched by a finger, the PE film on an upper surface of the glass or transparent plastic plate is bent, and the two surfaces of the glass or transparent plastic plate come in contract with each other. Thus, due to a resistive component of the two surfaces, parallel connection of resistors is formed, and a change in resistance occurs.
In this case, a change in voltage occurs due to the current that flows through both ends of the resistive film. The position of the touching finger can be known by a degree of change in voltage. Due to characteristics of the pressure sensitive type touch screen, the two surfaces of the glass or transparent plastic plate must come in contact with each other so that pressure can be recognized. Thus, the pressure sensitive type touch screen is able to operate under pressure generated by a ball pen or other materials. The pressure sensitive type touch screen is used in most full touch type domestic mobile phones. The pressure sensitive type touch screen has advantages of a low price and the capability to write in a small column by writing using a stylus pen. On the other hand, because it uses pressure, the pressure sensitive type touch screen has disadvantages that if a strong pressure is applied to the touch screen, it is not recognized, and it is relatively less sensitive to touch compared to the capacitive type touch screen.
The capacitive type touch screen, unlike the pressure sensitive type touch screen using pressure, is formed of glass having high conductivity, such as indium tin oxide (ITO). The principle of the capacitive type touch screen is to recognize a change in current that flows through the surface of glass by attaching sensors to four corners of the glass.
The instant a finger touches a screen, electrons flowing through the glass flow into a body through the finger, and the changed position of the electrons is sensed by the sensors such that the touch screen operates. The capacitive type touch screen is characterized in that a sense of manipulation and scrolling are more smooth than in the pressure sensitive type touch screen, and multi-touch whereby several points can be touched, can be performed. The capacitive type touch screen operates using a changing quantity of current, and thus does not operate by a fingernail through which no current flows, or a stylus pen. Also, since the sensors are sensitive, they may be affected by peripheral devices.
The capacitive type touch screen is capable of performing multi-touch, unlike the pressure sensitive type touch screen. If the screen is touched by an object through which electricity flows, such as a finger, using only one layer covered with an electro-conductive material, the flow of electricity is changed and thus the touch can be recognized.
In the capacitive type touch screen using an electrostatic force, each cell of a sensing wiring is connected to a controller of a touch screen panel. The controller transmits a measurement signal to each cell corresponding to the sensing wiring and receives a sensing signal generated by a human body when touch occurs on the surface of the touch screen, from the sensing wiring. Sensing signals of horizontal-axis and vertical-axis touch sensing wirings are coordinated so that a touch position can be detected. The capacitive type touch screen has a complicated structure, high manufacturing cost, and a low sensing efficiency due to noise generated by a small capacitance value, in comparison with the resistive film type touch screen. However, the capacitive type touch screen has high transmissivity and operates with a very small pressure compared to the resistive film type touch screen, and thus has good durability.
In a capacitive type touch screen panel, when the human body does not contact the panel, electrostatic capacitance values of sensors are zero or very small, and when the human body contacts the panel, electrostatic capacitance values corresponding to an area formed by a touch pad and the human body are sensed. The shape of the touch pad that senses an electrostatic capacitance may be configured in the following various ways. That is, the touch pad may be a cell type touch pad configured according to position, a touch pad, a contact width that varies depending on position, or an arrangement type touch pad in which wirings having uniform widths are perpendicular to each other. Among these, the arrangement type touch pad in which a horizontal-axis wiring and a vertical-axis wiring are perpendicular to each other is the most commonly-used type.